This invention relates to liquid chromatographic methods and apparatuses.
Inexpensive liquid chromatographic apparatuses have been developed and are in use, particularly for preparatory chromatography where the emphasis is on quickly obtaining relatively large samples at low cost. Such systems generally include at least one solvent reservoir, a pump, a controller, a chromatographic column, a collector and usually a detector. Commonly, provision is made for a gradient to be developed and such gradient systems require at least two solvent reservoirs and some mechanism for mixing the solvent from each of the two reservoirs together to form a gradient for application to the column.
The prior art apparatuses have a disadvantage in that they are not as inexpensive as desired or require a longer period of time than desired for the separation.
Accordingly, it is an object of the invention to provide a novel chromatographic system and method.
It is a still further object of the invention to provide a low-cost method of providing substantial amounts of solvent to a chromatographic system.
It is a still further object of the invention to provide an inexpensive gradient chromatographic system.
It is a still further object of the invention to provide a low-cost detection system equipped to handle relatively large amounts of solvent and separated materials.
It is a still further object of the invention to provide an economical system for driving multiple inexpensive pumps while avoiding damage from excessively high pressures such as may be caused by blockage of liquid jamming of any one of the multiple pumps.
In accordance with the above and further objects of the invention, a chromatographic system includes a plurality of pumps, all driven together by a single pump motor for drawing solvent from solvent reservoirs, pumping the solvent through a plurality of columns for separation of sample, pumping the solvent and solute through a plurality of detectors for detecting solute and pumping the solute into a fraction collector for collection. The solvent is pulled from the reservoir through a plurality of outlets of a manifold so that a plurality of flow streams may be pulled into the corresponding plurality of pumps from one or more solvent reservoirs. The pumps may each receive the combined output of a plurality of different solvent reservoirs in controlled ratios, and in the preferred embodiment, with multiple charges of each solvent for each pump cycle to form a gradient and the different solvents in the case of such a gradient are mixed in the path between a flow inlet conduit to the pump and the pump outlet with the pump cylinder and inlet tube being dimensioned to provide adequate mixing during refill of the pump. The ratios of solvents are controlled by a solenoid operated valve in the preferred embodiment. Mixing in the pump cylinders is aided by a rapid refill stroke pulling solvent into an off-center inlet port of the piston pumps, causing turbulence.
With this arrangement, a single motor is able to drive a multiplicity of pumps which together can supply a large amount of solvent to a number of columns simultaneously. In the preferred embodiment, at least two different reservoirs pull solvents and different gradients are applied to at least some columns. However, embodiments in which the same solvent is applied to each column is possible and a gradient may be applied to some columns and a single solvent to others. In one embodiment, the gradient is formed without separate mixers and the mixing is done in the pump and the inlet to the pump and/or other equipment associated with the system. In the event of over-pressure in the liquid, which may be indicative of blockage or jamming in the system, the system senses the over-pressure and compensates by: (1) reducing the flow rate until the pressure is reduced; or (2) by stopping the pump or pumps and providing an indication of over-pressure so the problem can be corrected such as by attaching a tube to drain the cylinder of the pump; or (3) by manually disconnecting or removing the malfunctioning portion of the system; or (4) by continuing the motion of the motor and automatically by-passing any column causing that over-pressure for that pump, such as for example with a fluid pressure release valve.
An inexpensive detecting arrangement is utilized that comprises a light source which focuses light from a central spot on a lamp for stability and selects the frequency of light with a diffraction grating, reflecting the selected light through a slot and onto a plurality of light conductors. The selected light is transmitted through the light conductors to flow cells. Each flow cell has within it two light guides that are aligned and have a space between them for some of the fluid from the chromatographic column to flow. One of the light guides in each of the flow cells receives light from a corresponding one of the light conductors and transmits it to the other light guide through the effluent from the column without intervening focusing means to provide light-guide to light-guide communication in the flow cell through the fluid passing in between the two light guides. The light that is not absorbed in the flow cell is detected by photodiodes located directly against the receiving light guides.
From the above description, it can be understood that, the chromatographic system and chromatographic method of this invention is low cost and yet provides substantial yield in a short time.